Earlier today AVO lowered the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY for Cleveland. No further explosions have been detected at Cleveland since March 13, and we have no evidence that lava-dome growth has renewed since then.

Recent short explosions on March 8, 10, and 13 were detected by seismic and infrasound networks, but clouds prevented observation of the resulting plumes in satellite images. Absence of significant deposits on the volcano suggest that the explosions have been relatively ash-poor. Prior to this March activity, several small explosions were also detected in December 2011. An event on December 29 produced a small ash cloud that rose about 15,000 feet above sea level and drifted out over the North Pacific. The onset of explosive activity in December followed about a four-month period of slow, intermittent effusion of lava into the summit crater.

Additional sudden explosions of blocks and ash are still possible with little warning. It is possible for associated ash clouds to exceed 20,000 feet above sea level. If a larger ash-producing event occurs, seismic, infrasound, or volcanic lightning networks should detect the event and alert AVO staff. There is no real-time seismic monitoring network on Mount Cleveland so AVO is unable to track activity in real time.

Cleveland volcano forms the western half of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. It is located about 75 km (45 mi.) west of the community of Nikolski, and 1500 km (940 mi.) southwest of Anchorage. The volcano's most recent significant eruption began in February, 2001 and it produced 3 explosive events that produced ash clouds as high as 12 km (39,000 ft) above sea level. The 2001 eruption also produced a rubbly lava flow and hot avalanche that reached the sea. The most recent minor ash emissions were observed in January and June 2009.

Seismic activity at Iliamna Volcano remains above background, though lower than the levels recorded earlier in the month when AVO first raised the Color Code/Alert Level to YELLOW/ADVISORY. During the past week, small earthquakes continued to occur below the general vicinity of the volcano at depths mostly less than 4 km (2.5 miles) below sea level.

A flight to measure levels of gas emission and make visual observations of the summit area occurred on Saturday, March 17. Data from the flight indicate that the volcano is emitting elevated levels of sulfur dioxide and carbon dioxide, consistent with a magmatic source. It is not known, however, if this is a newly intruded magma, or whether new pathways for gas from preexisting magma have caused the increased gas flux. The amount of gas being emitted is broadly similar to levels seen in 1996-1997, when a likely magmatic intrusion but no eruption occurred at the volcano.

Observers on the flight saw vigorous and plentiful fumaroles (gas vents) at the volcano's summit, consistent with the elevated gas emissions. No obvious signs of recent rockfall, large areas of newly exposed bedrock, or unusual disturbance of the glacial ice were observed. Some deformation of the ice at the headwall of the Red Glacier on the east side of the summit was seen, but it is not clear whether this is related to the current volcanic unrest; avalanching of the glacier is common on this very steep area and was last seen in 2008.

The current activity at Iliamna does not indicate an imminent or certain eruption. A similar seismic swarm at Iliamna in 1996-1997 was not followed by eruptive activity. Prior to an eruption, AVO would expect to see a further increase in earthquake activity.

Iliamna volcano is located on the western side of lower Cook Inlet in the Lake Clark National Park. Iliamna is a snow-covered stratovolcano which rises 10,020 feet above sea level. Although steam plumes occur on its eastern flanks, there has been no historic volcanic activity at Iliamna. Iliamna is located 225 km (140 miles) southwest of Anchorage and 113 km (70 miles) southwest of Homer.

OTHER ALASKA VOLCANOES

Seismic activity is monitored in real time at 29 volcanoes in Alaska. Satellite images of all Alaskan volcanoes are analyzed daily for evidence of ash plumes and elevated surface temperatures. Some volcanoes may currently display anomalous behavior but are not considered to be at a dangerous level of unrest. Akutan, Aniakchak, Augustine, Dutton, Fisher, Fourpeaked, Gareloi, Great Sitkin, Griggs, Isanotski, Kanaga, Katmai, Mageik, Makushin, Martin, Novarupta, Okmok, Pavlof, Redoubt, Shishaldin, Snowy, Spurr, Tanaga, Trident, Ugashik-Peulik, Ukinrek Maars, Veniaminof, and Westdahl volcanoes are in color code GREEN and volcano alert level Normal. All are at or near normal levels of background seismicity. AVO did not detect ash plumes or significant elevated surface temperatures in the vicinity of any of these volcanoes.

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.

VOLCANO ALERT LEVELS

NORMALVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

ADVISORYVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

WATCHVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.

WARNINGHazardous eruption is imminent, underway, or suspected.

AVIATION COLOR CODES

GREENVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

YELLOWVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

ORANGEVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].

REDEruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].